The artificial magnetic conductors are better known by their acronym AMC. For more information on the principles of operation of these artificial magnetic conductors and their physical properties, reference can be made to the patent application WO 99 509 29 filed by Sievenpiper.
Typically, the artificial magnetic conductors exhibit two characteristic properties:                a high surface impedance Zs in a range of frequencies called “passband”, and        a resonance frequency f0, contained in the passband, for which the phase-shift is zero between an incident electromagnetic wave on the artificial magnetic conductor and the reflected electromagnetic wave.        
The surface impedance Zs is defined by the following ratio: Zs=Etan/Htan, in which:                Etan is the component of the electrical field of the incident electromagnetic wave tangential to the face of the artificial magnetic conductor, and        Htan is the component of the magnetic field of the incident electromagnetic wave tangential to the surface of the artificial magnetic conductor.        
A surface impedance Zs is said to be “high” if its modulus is greater than the vacuum wave impedance (modulus of Zs>377 Ohms) and, preferably, several times greater than the vacuum wave impedance.
Known artificial magnetic conductors comprise:                a ground plane,        at least one first frequency-selective surface, transparent for certain wavelengths and reflecting for a range of wavelengths, this frequency-selective surface comprising an array of conductive resonant elements arranged alongside one another in at least two different directions parallel to the ground plane.        
These artificial magnetic conductors are used to produce antennas. For example, known antennas comprise:                an artificial magnetic conductor exhibiting a resonance frequency f0,        a radiant conductor suitable for radiating or for receiving electromagnetic waves at a working frequency fT of between 0.5f0 and 2f0, this conductor extending in a plane parallel to the artificial magnetic conductor and being separated from the closest frequency-selective surface of this artificial magnetic conductor by a distance less than λ0/10, in which λ0 is the wavelength of an electromagnetic wave of frequency f0.        
There is a strong demand to miniaturize the antennas. These days, it is possible to use radiant conductors with a length less than λT/4 or λT/10, where λT is the wavelength at the working frequency fT of the antenna. It is therefore also desirable to reduce the size and the footprint of the artificial magnetic conductors. For this, the dimensions of the resonant elements have to be reduced. Now, when the dimensions of the resonant elements are reduced, the passband of the artificial magnetic conductor also decreases. This is not desirable.
Moreover the lower the resonance frequency f0 desired for the artificial magnetic conductor, the greater the size of the resonant elements. Thus, to miniaturize an artificial magnetic conductor, it is also desirable to have resonant elements which, with a size equal to the resonant elements of the known artificial magnetic conductors, make it possible to obtain a lower resonance frequency f0.